Helmet



FIG. 1 is a front right perspective view of a helmet comprising the new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a right-side elevation view thereof, the left side elevation view being a mirror image thereof;

FIG. 4 is a rear elevation view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom view thereof.

The environmental structure shown in broken lines forms no part of the claimed design. 

CLAIM The ornamental design for a helmet, as shown and described. 